Frequency modulation transmission system



Aug. 22, 195o J. L. HURAULT FREQUENCY MODULATION TRANSMISSION SYSTEM Filed Feb. 26, 1948 Sheets-Sheet l INVENTOR ATTORNEY A11g 22, 1950 J. L. HURAULT FREQUENCY MoDULA'rIoN TRANSMISSION SYSTEM s sheetsshet s Filed Feb. 26, 1948 Tua E wl o j R n. J m M J M. a a w. n 7 6 E 2 N J M. l- A. m g n P n 6 7. N R .n u f rm. as .m0 F

FREQUENCY Patented ug. 22, 1950 FREQUENCY MODULATION TRANSMISSION SYSTEM Jean Louis Hurault, Paris, France, assignor to Compagnie Industrielle des Telephones, Paris, France, a corporation of France Application February 26, 1948, Serial N o. 11,223 In France February 20, 1947 Section 1, Public Law 690, August 8, 1946 Patent expires February 20, 1967 (ci. asa-2s) 3 Claims.

The present invention has for an object to provide a frequency modulating transmitting system in which is used, in transmission, for signal generation, a single tube with fixed transconductance, which permits obtaining a relation for the variation of the frequency of the modulated current as a function of the applied signal amplitude which is perfectly' dened and independent, within wide limits, of the tube power supply conditions.

Such a system eliminates using tubes of variable mu or variable transconductance as of variable pitch grid, the characteristics of which present large Variations as a function of time, as well as a function of the voltages applied to their various electrodes, which is likely to appreciably interfere with proper transmitter operation.

The system constituting the object of the present invention, includes an oscillator tube, in which the coupling between the grid circuit and the plate circuit is ensured by two circuits, one of which has a variable attentuation as a function The quadripole I is constructed so as to cause a dephasing or phase displacement between the output voltage and the input voltagewhich phase displacement is variable as a function of the frequency. This dephaser quadripole i can be constituted, for instance, by means of a lattice band pass filter half unit of constant K type, of which the branches are respectively constituted by a resonant circuit and by an antiresonant circuit; Such a half unit affects for a given frequency fg, the actual phase displacement of the output voltage varying from ir/2 to -l-1r/2 in the freof the amplitude of the output signal causing 4 the frequency variations of the modulated current output.

In the drawing:

Fig. 1 shows a circuit of a frequency modulation transmitter according to the present invention;

Fig. 2 shows the variation of phase as a function of frequency caused by one of the grid-plate coupling circuits;

Fig. 3 is a vector diagram showing voltage relations of the grid input voltages;

Fig. 4 is a circuit diagram of a modified form of transmitter using for the dephaser, a transformer and a particular type of lattice filter, and using a ring modulator;

Fig. 5 shows another modified form of transmitter having different arrangement and connections of the ring modulator through condensers;

Fig. 6 is a block diagram which shows one type of receiving apparatus for the present system, using two receiving channels; and

Fig. 7 shows in detail another type of receiving apparatus, using a ring modulator.

Figure 1 shows as an example one embodiment quency band limited by the extreme frequencies fa, fb, and cancelling out to zero for frequency fo. The constant K filter of any class is a ladder type network of reactances having the property that the productof its series impedance and its shunt impedance is a constant K independent of frequency. Such filters are well known in the literature, and are described, for instance, by Zobel, Bell System Technical Journal, page 4, January, 1923, also in Zobel Patents 1,509,184; 1,557,229; 1,850,146, and in the book by T. E. Shea, Transmission Networks and Wave Filters, New York, 1946 (page 221).

'Ihe second coupling circuit is constituted by quadripoles 2, 3 and 4. Quadripole 2 is an adjustable attenuation line, 3 is a dephaser phase transformer affecting by a constant retarding angle, 1r/2 per example, the outgoing voltage relatively to the incoming voltage, and causing also an increasing attenuation with the frequency, and 4 is a modulator controlled by the input signal applied to terminals 5 and 6, and constituted, for example, by a ring modulator, producing at its output terminals, a variable Voltage, in phase or in phase opposition with the voltage applied at the input.

The increase of attenuation of the dephasing phase transformer 3 as a function of the frequency has for an object attenuating the harmonies produced in the oscillating tube, and as they are not subjected to the same phase displacement in the dephaser, they appear amplied at the output of the oscillator.

As a form of embodiment, such phase transformer may be constituted by two gamma cells comprising resistances in the series arms and capacities in the parallel arms. When the operating frequency of a dephasing phase transformer so constituted is such that the impedance of the parallel arms is equal to the resistance of the series arms, the output voltage V2 is related to the input voltage V1 by the formula:

V This formula shows that the phase difference for the considered frequency is 1r/2 and the attenueton 1.1 neper.

For the'- higher frequencies, cali:ulatlo'n. slmws` that harmonic 2 i'sattenuated IyILQfnepers: and;

harmonic 3 by 2.49 nepers.

The operation of such a system will be betterunderstood by referring to theiligures' 2. and:.3`.

Figure 2 shows as a function of the frequency.; the phase variation effectedfby a1 currenttraversing the dephasing quadripole.4 I.v

Figure 3 is a vector diagram which showsftheJ combination of the voltages acting ont the. grid. of.

tube L.

In Figure 3 OX shows the. voltage P'p applied to the plate, OA the voltage Uratthe' output terminals of quadripole I, OB' the' voltage U2 at the output terminals of quadripole' 2', and= OC the resulting voltageUg applied to the grid.

New;A it isv well; lmown;k that. the: frequerccy of the oscillations can (be. maintainedinan oscillator. is thel frequency for Whiclrntheretexists exact phase.Y opposition .betweenthe-.gridandi plate voltages.

rlherefore, vector. OC (Eig 3:)v representing.: the phase of voltage Uy. acting on; the grid.. must make an angle of 180 with OX, forthefrequen.- cy atwhich the generator'is'to oscillate.

In` fact, voltage Uy. isthe: resultaniroi com.- ponent voltages; OA`= Uir and B: 112;. The. volt'- ages at theterminals Ontheplate sidesrof quadri.- pole I and. 4-` arel in phasewith plate. voltage.' Up due` to the. shuntI resista'ncesi connected. across those'.A terminals; the d'eplia'sing; phase: dierence introduced-f by. phase'. transformer 3v is: supposed to: be equal to 1r/2 on the g'ure; Butlthe direc'- ti'on of OB'l would have to be: inverted 11i-'terminal voltage. 5 and.'` S should be inverted..

With: no' Uzavoltage ati thel output terminals of' quadripole. 2', whichE corresponds, closely to. the passage through zero of;v the1 modulating: voltage; the. grid voltage Ug issreducedfvto tlievol'tage; U31 and. must be in phase oppostionfwithi plate voltage Up; due toa suitable.- selection. ot thefc'o'n.- nections ofthe output. terminalsnof quadripole I, suchf oppositionzis producedI for frequei'myl fmv When theY voltage U2 atthe output terminals of quadripole 2 assumes af. value different. from zero,- in quadrature in one'. directiorn ou: the other with. plate' voltage: Up.; the' corresponding: oscil'e lator frequency becomesnxeddueftorthe: condie tion that the; resultant of U2; combined witlr. U1 (the Value of that' voltage Ui: being. determined as aJ function of. the frequcncy)f should.:` be: in phasev opposition with plate? voltage-Up.-

Figure 4 shows.v a modiied fornr. off.' embodiment of the generator according' to the.` invention` In Figure 4,. 9.* shows. a. transformer: designedi to cause phase oppositioit betweeni the grid voltage andthe tube plate voltage; The variablel phase difference quadripole or four terminalznetworlc. I (Figure l) is-.constitutedaby a constant K tnperlattice band pass filter half unit; The input voltage; appliedv toinput terminals I0 anrlIIr, centrols a modulator (modulatorfal: ot Figure' 1*); which is in the selected example;,a; ringz modulator constituted by four rectierf' elements 41|-, 42,. 43, 44'.

The dephasing phasey transformer: (phase transformer 2;.3' of Figurel); is constituted by: a single capacityf :i8A and: apotentiometer- 31;; the latter is used asy anattenuator .andi permits ad.- justment of the extent of the frequency deviation.

Figure represents a modified form of embodiment of the generator according to' the-pres audace entinvention; rIfhe arrangement is different from. thatof Figure 4 by the type and connections of the ring modulator; the input voltage being applied to terminals I2 and I3. Such arrangement permits a continuous variation of the voltage applied to the grid tube through the dephasing phase transformer.

Figure 6 represents the .block diagram of the receiving. `circuit arrangement. In Figure 6, I4 and I5 are the terminals to which is applied the incoming frequency wave, I6 is a lter providing a quick phase variation about the mean frequency (actual phase difference variation of in the pass band); Il is a phase transformer producing a phase difference practically constant as a function of the frequency; I8 and I9 are two amplifiers, and 2 a conventional modulator. The. low frequency current is taken off atv the terminals 2l, 22.

Figure 7 represents a type of embodiment of the'receiving part, of the system of the present invention, and' using a ring modulator.

It can readily be demonstrated that the system; which is the object of the present invention, permits when the phase diierences are identical at the transmitter and .at the receiver, obtaining a perfectly linear transmission for low initial signal amplitudes, corresponding to small frequency deviations.

What I claim is:

l. In a system of frequency modulation transmission, an oscillator tube with xed transconductance, a rst coupling circuit connected between the grid and thev plate of said tubev comprising a two-winding transformer, one of whose windings is inserted in the plate circuit. oi' the tube, a lattice constant K type band.- pass lter half unit, the other winding of said transformer being connected to the grid of said tube through said unit, and a second coupling circuit between the grid and the plate of said tube comprising a modulator, said modulator having carrier input connections, a control circuit, and an output'circuit, said. carrier input connections being inserted in the plate circuit of said tube, said control circuit being connected to receive a modulating signal'voltage, a dephaser adapted to cause a constant dephasing of substantially degrees, and said output circuit being connected to. the grid' of said tube through said depliaser.v

2. A system according to claim l", said'1nod ulator being a ring modulator.

3. A system according to claim 1', said modulator being a ring modulator comprising four rectifier elements connected in bridge, a center tapped transformer winding connected toA two terminals of` said bridge, and two series connected' capacities connected to the other two terminals of said bridge, the modulating input signal being applied to said last mentioned: terminals across said condensers, and the plate of said tube being connected to the commenterminal of" said two condensers.

JEAN LOUIS HURAULT;

REFERENCES' CITED The following references are of record v in the ile of` this patent:

UNI'ElI)y STATES PATENTS Number Name Date 2,347,398I Crosby Apr. 25, 1944 2,458,574 Dow- Jan. 11-. 11949 

